This invention relates to the production of aromatic phosphites and in particular to an improved method for the production of aromatic phosphites, as well as to aromatic phosphites produced thereby.
Aromatic phosphites are useful intermediates in the formation of dicarboxylic acid derivatives such as adiponitrile. Hitherto, the phosphite has been obtained by reacting phosphorus trichloride (PCl3) and an aromatic hydroxy compound, in the presence of a solvent such as toluene and an alkyl amine such as triethylamine, to remove hydrogen chloride from the reaction. This reaction is carried out at low temperature, generally at about xe2x88x9220xc2x0 C. or less.
When triethylamine is added to the above reaction mixture, it precipitates out of solution as the hydrochloride and forms a thick slurry which can coat the sides of reaction vessels and impede the manufacturing process. The precipitation is exacerbated when the production is scaled-up, making the slurry impossible to stir adequately without the use of special equipment such as a multiple impeller.
The applicants have devised an improved process in which the disadvantages of the hitherto-used method are minimised.
Accordingly, the present invention provides an improved method for the production of an aromatic phosphite from an aromatic hydroxy-compound and a phosphorus trihalide in the presence of a tertiary amine and a non-protic solvent which is mobile below xe2x88x9220xc2x0 C., wherein the improvement comprises the use, as said tertiary amine, of a tri-propyl or a tributyl amine.
The present invention also provides an aromatic phosphite made by the improved method described in the immediately-preceding paragraph.
The tertiary amine may be tri-n-propylamine, tri-iso-propylamine, tri-n-butylamine, tri-iso-butylamine, or tri-t-butylamine.
The phosphorus trihalide may be phosphorus trichloride or phosphorus tribromide. Preferably the phosphorus trihalide is phosphorus trichloride.
The aromatic hydroxy-compound may be a substituted or unsubstituted aromatic mono-or polyhydric alcohol, for example a substituted phenol (e.g. thymol) or an unsubstituted phenol, or a substituted or unsubstituted diphenol, resorcinol or quinone. Alternatively, the aromatic hydroxy-compound may have a condensed ring system and may be, for example, a substituted or unsubstituted monohydric or polyhydric naphthol, anthrol or phenanthrol.
The solvent may be, for example, an aromatic compound such as toluene, xylene, monochlorobenzene, dichlorobenzene, or 1, 4, 5-trimethyl benzene.
Preferably the solvent is used in the minimum amount to maintain the reaction in a mobile phase.
A preferred embodiment of the invention will now be illustrated, merely by way of example, as follows.